The present invention relates to apparatus for depositing liquid droplets on a moving receiving surface, and more particularly to improvements in apparatus which can form part of image construction systems using multiple arrays of drop generators. For example, the apparatus of the present invention may be utilized to create a pattern or image as in a printing operation.
U.S. Pat. No. 3,560,988 to Krick discloses an apparatus for high-speed precision placement of liquid droplets on a movable member, e.g., a web of paper having a receiving surface for droplets. The apparatus comprises a device for projecting drops onto the receiving surface at an angle other than 90.degree. in order to impart to the drops a substantial velocity component in the direction of relative movement between the drop generator and the receivng surface. The purpose of such inclination of the direction of drop travel relative to the direction of travel of the receiving surface is to reduce the velocity of relative movement between the receiving surface and the drops and to thus reduce the likelihood of smearing or distortion of drops on impact against the receiving surface.
Problems arise when the member is moved at such a speed that a gaseous boundary layer develops along the receiving surface. The droplets must penetrate through the boundary layer and are thereby deflected and deformed so that they produce on the receiving surface dots of blurred non-circular outline. The propulsion of drops at an acute angle to the direction of travel of the member is of no help because the drops invariably produce marks of oval outline.